11 Com is a low metallicity star with an iron abundance about half that of the Sun.[2]

11 Com has a substellar companion with a minimum mass of about 19.4 Jupiter masses orbiting at about 1.3 AU around it. The object's mass is well within the range of deuterium burning brown dwarfs.[4][5]

1.
Constellation
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A constellation is formally defined as a region of the celestial sphere, with boundaries laid down by the International Astronomical Union. The constellation areas mostly had their origins in Western-traditional patterns of stars from which the constellations take their names, in 1922, the International Astronomical Union officially recognized the 88 modern constellations, which cover the entire sky. They began as the 48 classical Greek constellations laid down by Ptolemy in the Almagest, Constellations in the far southern sky are late 16th- and mid 18th-century constructions. 12 of the 88 constellations compose the zodiac signs, though the positions of the constellations only loosely match the dates assigned to them in astrology. The term constellation can refer to the stars within the boundaries of that constellation. Notable groupings of stars that do not form a constellation are called asterisms, when astronomers say something is “in” a given constellation they mean it is within those official boundaries. Any given point in a coordinate system can unambiguously be assigned to a single constellation. Many astronomical naming systems give the constellation in which an object is found along with a designation in order to convey a rough idea in which part of the sky it is located. For example, the Flamsteed designation for bright stars consists of a number, the word constellation seems to come from the Late Latin term cōnstellātiō, which can be translated as set of stars, and came into use in English during the 14th century. It also denotes 88 named groups of stars in the shape of stellar-patterns, the Ancient Greek word for constellation was ἄστρον. Colloquial usage does not draw a distinction between constellation in the sense of an asterism and constellation in the sense of an area surrounding an asterism. The modern system of constellations used in astronomy employs the latter concept, the term circumpolar constellation is used for any constellation that, from a particular latitude on Earth, never sets below the horizon. From the North Pole or South Pole, all constellations south or north of the equator are circumpolar constellations. In the equatorial or temperate latitudes, the term equatorial constellation has sometimes been used for constellations that lie to the opposite the circumpolar constellations. They generally include all constellations that intersect the celestial equator or part of the zodiac, usually the only thing the stars in a constellation have in common is that they appear near each other in the sky when viewed from the Earth. In galactic space, the stars of a constellation usually lie at a variety of distances, since stars also travel on their own orbits through the Milky Way, the star patterns of the constellations change slowly over time. After tens to hundreds of thousands of years, their familiar outlines will become unrecognisable, the terms chosen for the constellation themselves, together with the appearance of a constellation, may reveal where and when its constellation makers lived. The earliest direct evidence for the constellations comes from inscribed stones and it seems that the bulk of the Mesopotamian constellations were created within a relatively short interval from around 1300 to 1000 BC

2.
Coma Berenices
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Coma Berenices is an ancient asterism in the northern sky which has been defined as one of the 88 modern constellations. It is located in the fourth quadrant, between Leo and Bootes, and is visible in both hemispheres. It was introduced to Western astronomy during the third century BC by Conon of Samos and its name means Berenices Hair in Latin and refers to Queen Berenice II of Egypt, who sacrificed her long hair as a votive offering. Coma Berenices is the modern constellation named for an historic figure. It was further corroborated as a constellation by Gerardus Mercator and Tycho Brahe, three of the constellations stars are visible to the naked eye, Alpha Comae Berenices, Beta Comae Berenices and Gamma Comae Berenices. They form a 45-degree triangle, from which Berenices imaginary tresses hang, the constellations brightest star is Beta Comae Berenices, a 4. 2-magnitude main sequence star similar to the Sun. Coma Berenices contains the North Galactic Pole and one of the richest known galaxy clusters, Galaxy Malin 1, in the constellation, is the first known giant low-surface-brightness galaxy. Supernova SN 2005ap discovered in Coma Berenices is the brightest known, the star FK Comae Berenices is the prototype of an eponymous class of variable stars. The constellation is the radiant of one meteor shower, Coma Berenicids, Coma Berenices has been recognized as an asterism since the Hellenistic period, and is the only modern constellation named for an historic figure. It was introduced to Western astronomy during the third century BC by Conon of Samos, Berenice vowed to sacrifice her long hair as a votive offering if Ptolemy returned safely from battle during the Third Syrian War. In Callimachus poem, Aetia, Berenice dedicated her tresses to all the gods, in the Latin translation of the poem by the Roman poet Catullus and in Hyginus De astronomica, she dedicated her tresses to Aphrodite and placed them in the temple of Arsinoe II at Zephyrium. According to De astronomica, by the morning the tresses had disappeared. Conon proposed that Aphrodite had placed the tresses in the sky as an acknowledgement of Berenices sacrifice, Callimachus called the asterism plokamos Berenikēs or bostrukhon Berenikēs in Greek, translated into Latin as Coma Berenices by Catullus. Eratosthenes called it Berenices Hair and Ariadnes Hair, considering it part of the constellation Leo, the astronomer Geminus recognized it as a distinct constellation. Astronomer Ptolemy considered it part of Leo, and called it Plokamos, Coma Berenices became popular during the 16th century. In 1515, a set of gores by Johannes Schöner labelled the asterism Trica, in 1536 it appeared on a celestial globe by Caspar Vopel, who is credited with the asterisms designation as a constellation. That year, it appeared on a celestial map by Petrus Apianus as Crines Berenices. In 1551, Coma Berenices appeared on a celestial globe by Gerardus Mercator with five Latin and Greek names, Cincinnus, caesaries, πλόκαμος, Berenicis crinis, mercators reputation as a cartographer ensured the constellations inclusion on Dutch sky globes beginning in 1589

3.
Star
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A star is a luminous sphere of plasma held together by its own gravity. The nearest star to Earth is the Sun, many other stars are visible to the naked eye from Earth during the night, appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth. Historically, the most prominent stars were grouped into constellations and asterisms, astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. However, most of the stars in the Universe, including all stars outside our galaxy, indeed, most are invisible from Earth even through the most powerful telescopes. Almost all naturally occurring elements heavier than helium are created by stellar nucleosynthesis during the stars lifetime, near the end of its life, a star can also contain degenerate matter. Astronomers can determine the mass, age, metallicity, and many properties of a star by observing its motion through space, its luminosity. The total mass of a star is the factor that determines its evolution. Other characteristics of a star, including diameter and temperature, change over its life, while the environment affects its rotation. A plot of the temperature of stars against their luminosities produces a plot known as a Hertzsprung–Russell diagram. Plotting a particular star on that allows the age and evolutionary state of that star to be determined. A stars life begins with the collapse of a gaseous nebula of material composed primarily of hydrogen, along with helium. When the stellar core is sufficiently dense, hydrogen becomes steadily converted into helium through nuclear fusion, the remainder of the stars interior carries energy away from the core through a combination of radiative and convective heat transfer processes. The stars internal pressure prevents it from collapsing further under its own gravity, a star with mass greater than 0.4 times the Suns will expand to become a red giant when the hydrogen fuel in its core is exhausted. In some cases, it will fuse heavier elements at the core or in shells around the core, as the star expands it throws a part of its mass, enriched with those heavier elements, into the interstellar environment, to be recycled later as new stars. Meanwhile, the core becomes a remnant, a white dwarf. Binary and multi-star systems consist of two or more stars that are bound and generally move around each other in stable orbits. When two such stars have a close orbit, their gravitational interaction can have a significant impact on their evolution. Stars can form part of a much larger gravitationally bound structure, historically, stars have been important to civilizations throughout the world

4.
Elliptical galaxy
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An elliptical galaxy is a type of galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless brightness profile. Unlike flat spiral galaxies with organization and structure, they are more three-dimensional, without much structure and they are one of the three main classes of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae, along with spiral and lenticular galaxies. Elliptical galaxies range in shape from spherical to highly flat. Originally Edwin Hubble hypothesized that elliptical galaxies evolved into spiral galaxies, stars found inside of elliptical galaxies are much older than stars found in spiral galaxies. Elliptical galaxies are believed to make up approximately 10%–15% of galaxies in the Virgo Supercluster and they are preferentially found close to the centers of galaxy clusters. Elliptical galaxies are also called early-type galaxies, due to their location in the Hubble sequence, elliptical galaxies are characterized by several properties that make them distinct from other classes of galaxy. They are spherical or ovoid masses of stars, starved of star-making gases, the smallest known elliptical galaxy is about one-tenth the size of the Milky Way. The motion of stars in galaxies is predominantly radial, unlike the disks of spiral galaxies. Large elliptical galaxies typically have a system of globular clusters. The dynamical properties of galaxies and the bulges of disk galaxies are similar, suggesting that they may be formed by the same physical processes. The luminosity profiles of both elliptical galaxies and bulges are well fit by Sersics law, every massive elliptical galaxy contains a supermassive black hole at its center. Observations of 46 elliptical galaxies,20 classical bulges, and 22 pseudobulges show that each contain a black hole at the center, elliptical galaxies are preferentially found in galaxy clusters and in compact groups of galaxies. The traditional portrait of elliptical galaxies paints them as galaxies where star formation finished after an initial burst at high-redshift, elliptical galaxies typically appear yellow-red, which is in contrast to the distinct blue tinge of most spiral galaxies. In spirals, this blue color emanates largely from the young, very little star formation is thought to occur in elliptical galaxies, because of their lack of gas compared to spiral or irregular galaxies. However, in recent years, evidence has shown that a proportion of these galaxies have residual gas reservoirs. Researchers with the Herschel Space Observatory have speculated that the black holes in elliptical galaxies keep the gas from cooling enough for star formation. Elliptical galaxies vary greatly in size and mass with diameters ranging from 3000 lightyears to more than 700,000 lightyears. This range is broader for this galaxy type than for any other

5.
Spiral galaxy
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A spiral galaxy is a type of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and these are surrounded by a much fainter halo of stars, many of which reside in globular clusters. Spiral galaxies are named for the structures that extend from the center into the galactic disc. The spiral arms are sites of ongoing star formation and are brighter than the surrounding disc because of the young, hot OB stars that inhabit them. Roughly two-thirds of all spirals are observed to have a component in the form of a bar-like structure, extending from the central bulge. Our own Milky Way has recently confirmed to be a barred spiral. The most convincing evidence for its existence comes from a recent survey, performed by the Spitzer Space Telescope, together with irregular galaxies, spiral galaxies make up approximately 60% of galaxies in the local Universe. They are mostly found in low-density regions and are rare in the centers of galaxy clusters, Spiral arms are regions of stars that extend from the center of spiral and barred spiral galaxies. These long, thin regions resemble a spiral and thus give spiral galaxies their name, naturally, different classifications of spiral galaxies have distinct arm-structures. Sc and SBc galaxies, for instance, have very loose arms, whereas Sa, either way, spiral arms contain many young, blue stars, which make the arms so bright. A bulge is a huge, tightly packed group of stars, the term commonly refers to the central group of stars found in most spiral galaxies. Using the Hubble classification, the bulge of Sa galaxies is usually composed of Population II stars, further, the bulge of Sa and SBa galaxies tends to be large. In contrast, the bulges of Sc and SBc galaxies are much smaller and are composed of young, some bulges have similar properties to those of elliptical galaxies, others simply appear as higher density centers of disks, with properties similar to disk galaxies. Many bulges are thought to host a supermassive black hole at their centers, such black holes have never been directly observed, but many indirect proofs exist. In our own galaxy, for instance, the object called Sagittarius A* is believed to be a black hole. There is a correlation between the mass of the black hole and the velocity dispersion of the stars in the bulge. However, some stars inhabit a spheroidal halo or galactic spheroid, the orbital behaviour of these stars is disputed, but they may describe retrograde and/or highly inclined orbits, or not move in regular orbits at all. The galactic halo also contains many globular clusters, due to their irregular movement around the center of the galaxy—if they do so at all—these stars often display unusually high proper motion

6.
Messier 100
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Messier 100 is an example of a grand design intermediate spiral galaxy located within the southern part of constellation Coma Berenices. It is one of the brightest and largest galaxies in the Virgo Cluster, the galaxy was one of the first spiral galaxies to be discovered, and was listed as one of fourteen spiral nebulae by Lord William Parsons of Rosse in 1850. Two satellite galaxies named NGC4323 -connected with M100 by a bridge of luminous matter-, after the discovery of M100 by Méchain, Charles Messier made observations of the galaxy depicting it as a nebula without a star. He pointed out that it was difficult to recognize the nebula because of its faintness, William Herschel was able to identify a bright cluster of stars within the nebula during observations he did before John Herschel expanded the findings in 1833. With the advent of better telescopes, John Herschel was able to see a round, brighter galaxy, however, William Henry Smyth extended the studies of M100, detailing it as a pearly white nebula and pointing out diffuse spots. Five supernovae have been identified in the M100 galaxy, in March 1901 the first supernova of M100 was found, SN 1901B, a type I supernova found when magnitude 15.6 at a distance from its nucleus. SN 1914A was then discovered in February to March 1914, its type was undeterminable but was found when magnitude 15.7 at some distance from the center. The latest supernova was discovered February 7,2006, the star SN 2006X had a magnitude of 15.3 when discovered two weeks before fading to magnitude +17. SEDS, Spiral Galaxy 100 Messier 100 on WikiSky, DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images ESA/Hubble Messier 100

7.
Mass
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In physics, mass is a property of a physical body. It is the measure of a resistance to acceleration when a net force is applied. It also determines the strength of its gravitational attraction to other bodies. The basic SI unit of mass is the kilogram, Mass is not the same as weight, even though mass is often determined by measuring the objects weight using a spring scale, rather than comparing it directly with known masses. An object on the Moon would weigh less than it does on Earth because of the lower gravity and this is because weight is a force, while mass is the property that determines the strength of this force. In Newtonian physics, mass can be generalized as the amount of matter in an object, however, at very high speeds, special relativity postulates that energy is an additional source of mass. Thus, any body having mass has an equivalent amount of energy. In addition, matter is a defined term in science. There are several distinct phenomena which can be used to measure mass, active gravitational mass measures the gravitational force exerted by an object. Passive gravitational mass measures the force exerted on an object in a known gravitational field. The mass of an object determines its acceleration in the presence of an applied force, according to Newtons second law of motion, if a body of fixed mass m is subjected to a single force F, its acceleration a is given by F/m. A bodys mass also determines the degree to which it generates or is affected by a gravitational field and this is sometimes referred to as gravitational mass. The standard International System of Units unit of mass is the kilogram, the kilogram is 1000 grams, first defined in 1795 as one cubic decimeter of water at the melting point of ice. Then in 1889, the kilogram was redefined as the mass of the prototype kilogram. As of January 2013, there are proposals for redefining the kilogram yet again. In this context, the mass has units of eV/c2, the electronvolt and its multiples, such as the MeV, are commonly used in particle physics. The atomic mass unit is 1/12 of the mass of a carbon-12 atom, the atomic mass unit is convenient for expressing the masses of atoms and molecules. Outside the SI system, other units of mass include, the slug is an Imperial unit of mass, the pound is a unit of both mass and force, used mainly in the United States

8.
Stellar classification
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In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the rainbow of colors interspersed with absorption lines, each line indicates an ion of a certain chemical element, with the line strength indicating the abundance of that ion. The relative abundance of the different ions varies with the temperature of the photosphere, the spectral class of a star is a short code summarizing the ionization state, giving an objective measure of the photospheres temperature and density. Most stars are classified under the Morgan–Keenan system using the letters O, B, A, F, G, K, and M. Each letter class is subdivided using a numeric digit with 0 being hottest and 9 being coolest. The sequence has been expanded with classes for other stars and star-like objects that do not fit in the system, such as class D for white dwarfs. In the MK system, a luminosity class is added to the class using Roman numerals. This is based on the width of absorption lines in the stars spectrum. The full spectral class for the Sun is then G2V, indicating a main-sequence star with a temperature around 5,800 K, the conventional color description takes into account only the peak of the stellar spectrum. This means that the assignment of colors of the spectrum can be misleading. There are no green, indigo, or violet stars, likewise, the brown dwarfs do not literally appear brown. The modern classification system is known as the Morgan–Keenan classification, each star is assigned a spectral class from the older Harvard spectral classification and a luminosity class using Roman numerals as explained below, forming the stars spectral type. The spectral classes O through M, as well as more specialized classes discussed later, are subdivided by Arabic numerals. For example, A0 denotes the hottest stars in the A class, fractional numbers are allowed, for example, the star Mu Normae is classified as O9.7. The Sun is classified as G2, the conventional color descriptions are traditional in astronomy, and represent colors relative to the mean color of an A-class star, which is considered to be white. The apparent color descriptions are what the observer would see if trying to describe the stars under a dark sky without aid to the eye, or with binoculars. However, most stars in the sky, except the brightest ones, red supergiants are cooler and redder than dwarfs of the same spectral type, and stars with particular spectral features such as carbon stars may be far redder than any black body. O-, B-, and A-type stars are called early type

9.
Virgo (constellation)
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Virgo is one of the constellations of the zodiac. Its name is Latin for virgin, and its symbol is ♍, lying between Leo to the west and Libra to the east, it is the second largest constellation in the sky. It can be found through its brightest star, Spica. The bright Spica makes it easy to locate Virgo, as it can be found by following the curve of the Big Dipper/Plough to Arcturus in Boötes and continuing from there in the same curve. Due to the effects of precession, the First Point of Libra and this is one of the two points in the sky where the celestial equator crosses the ecliptic This point will pass into the neighbouring constellation of Leo around the year 2440. Besides Spica, other stars in Virgo include β Virginis, γ Vir, δ Virginis. Other fainter stars that were given names are ζ Virginis, η Virginis, ι Virginis. The star 70 Virginis has one of the first known extrasolar planetary systems with one confirmed planet 7.5 times the mass of Jupiter, the star Chi Virginis has one of the most massive planets ever detected, at a mass of 11.1 times that of Jupiter. The sun-like star 61 Virginis has three planets, one is a super-Earth and two are Neptune-mass planets, SS Virginis is a variable star with a noticeable red color. It varies in magnitude from a minimum of 9.6 to a maximum of 6.0 over a period of one year. There are 35 verified exoplanets orbiting 29 stars in Virgo, including PSR B1257+12,70 Virginis, Chi Virginis,61 Virginis, NY Virginis, and 59 Virginis. Because of the presence of a cluster within its borders 5° to 12° west of ε Vir. Some examples are Messier 49, Messier 58, Messier 59, Messier 60, Messier 61, Messier 84, Messier 86, Messier 87, Messier 89, a noted galaxy that is not part of the cluster is the Sombrero Galaxy, an unusual spiral galaxy. It is located about 10° due west of Spica, NGC4639 is a face-on barred spiral galaxy located 78 Mly from Earth. Its outer arms have a number of Cepheid variables, which are used as standard candles to determine astronomical distances. Because of this, astronomers used several Cepheid variables in NGC4639 to calibrate type 1a supernovae as standard candles for more distant galaxies, Virgo possesses several galaxy clusters, one of which is HCG62. A Hickson Compact Group, HCG62 is at a distance of 200 Mly from Earth and it has a heterogeneous halo of extremely hot gas, posited to be due to the active galactic nucleus at the core of the central elliptical galaxy. M87 is the largest galaxy in the Virgo cluster, and is at a distance of 60 Mly from Earth and it is a major radio source, partially due to its jet of electrons being flung out of the galaxy by its central supermassive black hole

10.
Leo (constellation)
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Leo /ˈliːoʊ/ is one of the constellations of the zodiac, lying between Cancer the crab to the west and Virgo the maiden to the east. Its name is Latin for lion, and to the ancient Greeks represented the Nemean Lion killed by the mythical Greek hero Heracles as one of his twelve labors. The lions mane and shoulders also form an asterism known as The Sickle, Leo contains many bright stars, many of which were individually identified by the ancients. It is a double star divisible in binoculars, with a secondary of magnitude 7.7 and its traditional name means the little king. Beta Leonis, called Denebola, is at the end of the constellation to Regulus. It is a star of magnitude 2.23,36 light-years from Earth. The name Denebola means the lions tail, Algieba, Gamma Leonis, is a binary star with a third optical component, the primary and secondary are divisible in small telescopes and the tertiary is visible in binoculars. The primary is a giant star of magnitude 2.61. The unrelated tertiary,40 Leonis, is a star of magnitude 4.8. Its traditional name, Algieba, means the forehead, Delta Leonis, called Zosma, is a blue-white star of magnitude 2.58,58 light-years from Earth. Epsilon Leonis is a giant of magnitude 3.0,251 light-years from Earth. Zeta Leonis, called Adhafera, is a triple star. The brightest and only star designated Zeta Leonis, is a giant star of magnitude 3.65,260 light-years from Earth. The second brightest,39 Leonis, is widely spaced to the south,35 Leonis is to the north and of magnitude 6.0. Iota Leonis is a binary star divisible in amateur telescopes. To the unaided eye, Iota Leonis appears to be a star of magnitude 4.0. The system,79 light-years from Earth, has components of magnitude 4.1 and 6.7 with a period of 183 years, tau Leonis is a double star visible in binoculars. The primary is a giant of magnitude 5.0,621 light-years from Earth

11.
Stellar parallax
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Stellar parallax is parallax on an interstellar scale, the apparent shift of position of any nearby star against the background of distant objects. Stellar parallax is so difficult to detect that its existence was the subject of debate in astronomy for thousands of years. It was first observed by Giuseppe Calandrelli who reported parallax in α-Lyrae in his work Osservazione e riflessione sulla parallasse annua dall’alfa della Lira, then in 1838 Friedrich Bessel made the first successful parallax measurement ever, for the star 61 Cygni, using a Fraunhofer heliometer at Königsberg Observatory. Once a stars parallax is known, its distance from Earth can be computed trigonometrically, but the more distant an object is, the smaller its parallax. Even with 21st-century techniques in astrometry, the limits of accurate measurement make distances farther away than about 100 parsecs too approximate to be useful when obtained by this technique. Relatively close on a scale, the applicability of stellar parallax leaves most astronomical distance measurements to be calculated by spectral red-shift or other methods. Stellar parallax measures are given in the units of arcseconds. The distance unit parsec is defined as the length of the leg of a right triangle adjacent to the angle of one arcsecond at one vertex, because stellar parallaxes and distances all involve such skinny right triangles, a convenient trigonometric approximation can be used to convert parallaxes to distance. The distance is simply the reciprocal of the parallax, d =1 / p, for example, Proxima Centauri, whose parallax is 0.7687, is 1 /0.7687 =1.3009 parsecs distant. Stellar parallax is so small that its apparent absence was used as an argument against heliocentrism during the early modern age. James Bradley first tried to measure stellar parallaxes in 1729, the stellar movement proved too insignificant for his telescope, but he instead discovered the aberration of light, the nutation of Earth’s axis, and catalogued 3222 stars. The parsec is defined as the distance for which the annual parallax is 1 arcsecond, annual parallax is normally measured by observing the position of a star at different times of the year as Earth moves through its orbit. Measurement of annual parallax was the first reliable way to determine the distances to the closest stars, the first successful measurements of stellar parallax were made by Friedrich Bessel in 1838 for the star 61 Cygni using a heliometer. Being very difficult to measure, only about 60 stellar parallaxes had been obtained by the end of the 19th century, astrographs using astronomical photographic plates sped the process in the early 20th century. Automated plate-measuring machines and more sophisticated technology of the 1960s allowed more efficient compilation of star catalogues. In the 1980s, charge-coupled devices replaced photographic plates and reduced optical uncertainties to one milliarcsecond, stellar parallax remains the standard for calibrating other measurement methods. The angles involved in these calculations are very small and thus difficult to measure, the nearest star to the Sun, Proxima Centauri, has a parallax of 0.7687 ±0.0003 arcsec. This angle is approximately that subtended by an object 2 centimeters in diameter located 5.3 kilometers away

12.
Luminosity
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In astronomy, luminosity is the total amount of energy emitted by a star, galaxy, or other astronomical object per unit time. It is related to the brightness, which is the luminosity of an object in a spectral region. In SI units luminosity is measured in joules per second or watts, values for luminosity are often given in the terms of the luminosity of the Sun, which has a total power output of 7026384600000000000♠3. 846×1026 W. The symbol for solar luminosity is L⊙. Luminosity can also be given in terms of magnitude, the absolute bolometric magnitude of an object is a logarithmic measure of its total energy emission. In astronomy, luminosity is the amount of energy a body radiates per unit of time. It is most frequently measured in two forms, visual and bolometric, although luminosities at other wavelengths are increasingly being used as instruments become available to measure them, a bolometer is the instrument used to measure radiant energy over a wide band by absorption and measurement of heating. When not qualified, the term luminosity means bolometric luminosity, which is measured either in the SI units, watts, a star also radiates neutrinos, which carry off some energy, contributing to the stars total luminosity. In practice bolometric magnitudes are measured by taking measurements at certain wavelengths, a stars luminosity can be determined from two stellar characteristics, size and effective temperature. The former is represented in terms of solar radii, R⊙, while the latter is represented in kelvins. To determine a stars radius, two metrics are needed, the stars angular diameter and its distance from Earth, often calculated using parallax. However, for most stars the angular diameter or parallax, or both, are far below our ability to measure with any certainty, an alternate way to measure stellar luminosity is to measure the stars apparent brightness and distance. Because luminosity is proportional to temperature to the power, the large variation in stellar temperatures produces an even vaster variation in stellar luminosity. Because the luminosity depends on a power of the stellar mass. The most luminous stars are young stars, no more than a few million years for the most extreme. In the Hertzsprung–Russell diagram, the x-axis represents temperature or spectral type while the y-axis represents luminosity or magnitude. The vast majority of stars are found along the sequence with blue Class 0 stars found at the top left of the chart while red Class M stars fall to the bottom right. Certain stars like Deneb and Betelgeuse are found above and to the right of the main sequence, blue and white supergiants are high luminosity stars somewhat cooler than the most luminous main sequence stars. A star like Deneb, for example, has a luminosity around 200,000 L⊙, a type of A2

Hipparcos was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It …

Hipparcos satellite in the Large Solar Simulator, ESTEC, February 1988

Artist's concept of our Milky Way galaxy, showing two prominent spiral arms attached to the ends of a thick central bar. Hipparcos mapped many stars in the solar neighbourhood with great accuracy, though this represents only a small fraction of stars in the galaxy.

Image: Hipparcos insignia

Equirectangular plot of declination vs right ascension of stars brighter than apparent magnitude 5 on the Hipparcos Catalogue, coded by spectral type and apparent magnitude, relative to the modern constellations and the ecliptic

Proper motion is the astronomical measure of the observed changes in the apparent places of stars in the sky, as seen …

Relation between proper motion and velocity components of an object. At emission, the object was at distance d from the Sun, and moved at angular rate μ radian/s, that is, μ = vt / d with vt = the component of velocity transverse to line of sight from the Sun. (The diagram illustrates an angle μ swept out in unit time at tangential velocity vt.)

The astronomical unit (symbol: au or ua) is a unit of length, roughly the distance from Earth to the Sun. However, that …

The red line indicates the Earth–Sun distance, which on average is about 1 astronomical unit.

Transits of Venus across the face of the Sun were, for a long time, the best method of measuring the astronomical unit, despite the difficulties (here, the so-called "black drop effect") and the rarity of observations.